NATO reported that the Russian plane was identified as an Ilyushin-20 (IL-20), deployed from Kaliningrad.

"At 12:53 p.m. CET the IL-20 approached Estonian airspace from the northeast. The Russian aircraft entered Estonian airspace near the island of Saaremaa for a period of less than one minute, which represented an incursion of about 600 meters into NATO airspace," it said in a news release.

NATO spokesman Lt. Col. Jay Janzen said that the allied jets guided the Russian plane out of the airspace with help from an aircraft from non-allied Sweden. He also tweeted a picture of what the Russian intelligence gatherer looked like.

"Since the Ukraine crisis started, there haven’t been any incursions into the areas that NATO patrols as part of its air policing mission. This was the first one," Janzen said, according to The Washington Times.

The Associated Press reported that Estonian Foreign Ministry spokeswoman Mari-Liis Valter said on Wednesday that the violation is serious and "demands an explanation."

In a potentially related breach, the Swedish Navy has been searching for evidence that a foreign submarine crossed into its territorial waters near the Stockholm archipelago on Friday. It is suspected to have been a Russian submarine.